--> Monitoring Changes to Fault Transmissibility During Clay Smear Development in Direct Shear Experiments of Clastic-Argillaceous Sequences, Giger, Silvio; Ter Heege, Jan H.; Clennell, Michael B.; Ciftci, Bozkurt; Delle Piane, Claudio; Wassing, Brecht B.; Clark, Peter; Harbers, Craig; Beekman, Fred; Yamasaki, Tadashi, #90100 (2009)

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Monitoring Changes to Fault Transmissibility During Clay Smear Development in Direct Shear Experiments of Clastic-Argillaceous Sequences

Giger, Silvio1
 Ter Heege, Jan H.3
 Clennell, Michael B.1
 Ciftci, Bozkurt1
 Delle Piane, Claudio1
 Wassing, Brecht B.3
 Clark, Peter2
 Harbers, Craig2
 Beekman, Fred4
 Yamasaki, Tadashi4

1CSIRO Petroleum Resources, Kensington, WA, Australia.
2
CSIRO Exploration and Mining,
Kenmore, QLD, Australia.
3
TNO Built Environment and Geosciences,
Utrecht, Netherlands.
4
ISES
Research School, Amsterdam, Netherlands.

We have monitored the changes of fluid flow across evolving fault zones in cemented sand-clay sequences to displacements equivalent to several times the thickness of the embedded clay layer (Shale Smear Factor up to 10). A new type of direct shear sample cell was designed, capable of deforming intact sample blocks to large displacements under sealed conditions. The sealed cell fits within an existing large shear rig, which can apply normal and shear loads of 1 MN (fault-normal stress ≤30 MPa). The large sample blocks (24x15x12cm3) consisted of a pre-consolidated clay layer, which was synthetically cemented in quartz sand using a calcite in-situ precipitation technique. Material properties of the consolidated clays and cemented sand were determined separately by uniaxial/triaxial tests.

Fluid pressure inside the sandstone blocks could be monitored on either side of the clay bed and across the evolving fault zone through four injection/drainage ports. The development of fault zone geometries, clay smear structures, and associated changes to fluid flow were investigated by varying the clay consolidation state, the competence contrast of the mechanical layers, the inclination of the clay bed with respect to the shear plane, and the stress conditions.

The finite clay smear structures could be well resolved by stacking individual computer tomography scans to a comprehensive 3D model in reservoir modelling software. A discrete element numerical modelling package (PFC2D) was used to reproduce individual cross-sections in 2D. The PFC2D code was then combined with a finite difference package (FLAC) in a mesoscale model of a reservoir scale fault zone, with the ultimate aim to upscale the results to reservoir conditions. The quantitative findings of the physical experiments and sample scale discrete element models were incorporated in the mesoscale model.

Current results and ongoing research of our integrated experimental and modelling approach towards predictive fault seal assessment suggest a number of modifications to traditional algorithms such as Shale Gouge Ratio or Clay Smear Potential. Notably, the mechanical behaviour of faulted sequences and the deformation history need to be taken into account to improve the prediction of flow across and along faults. Our findings have relevance to subsurface groundwater flow, hydrocarbon exploration and production, and for CO2 for sequestration in faulted reservoirs.



AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil